Download Simple Machines and Work

Simple Machines and Work
Amy Johnson
Simple Machines
2 – Properties and Principles of
Force and Motion
 Strand
 Objective

2 – Forces effect motion
Concept F – Simple Machines (levers, inclined
planes, wheels and axles, pulleys) affect the
forces applied to an object and/or direction of
movement as work is done
 GLE
Lesson Overview
Types of Machines
Machine types
Simple vs. Compound

Machine that only
uses one movement
 Screwdriver =
turning
 Makes work easier,
faster, and changes
the direction of the
force or effort

Uses two or more
simple machines
 Can Opener =
wedge + wheel and
axle
 Makes work easier,
faster, and changes
the direction of the
force or effort
Work
 Force
causes an object to move in the
same direction as the force that is
applied
 The greater the force, the more work
that is done
 Work (in joules) = force X distance
(W=fd)
 Circle which involves more work?
 Lifting
a shoe or books to your waist
Practice
•Are both people doing work?
•Which picture is showing an example of
work?
•Explain how work is being done in one
picture but not the other.
ANSWER
Practice

If an lifted an object weighing 20 N through a
distance of 0.5 meters, how much work is
being done?

If a 60 newton man lifted his 10 newton
suitcase a distance of 0.5 meters and ran 25
meters, how much work is being done by the
man’s arms and by the man’s legs?
ANSWER
Machines affect work
 Change
size of force you apply
 Change direction of force
 Increases mechanical advantage
Mechanical Advantage (MA)


The number of times
the applied force is
increased by a machine
To figure the MA, you
must know the input
force and output force


Input force is the force
you apply
Output force is the force
exerted by the machine
MA = force out (N)
force in
(N)
FRICTION
 The
force that resists sliding motion
between two touching surfaces
 Ideally, the amount of work you do on
the machine should equal the amount of
work done by the machine.
 Unfortunately, friction changes some of
the input work into heat, therefore, the
work out is always less than the work in.
MAP Assesment
 A baseball
player swings his bat and
hits the baseball with a force of 8
newtons.
 How
much force does the ball exert on the
bat?
 Describe two forces acting on the ball as it
is flying through the air.
1.
 2.

MAP Scoring
8
newtons/8 N
 friction AND gravity
 Air
resistance is acceptable as friction.
WHOSE DOING WORK?
 No.
 The
man lifting the grocery bag is
showing work.
 The direction of the applied force and
motion must be the same. The man
carrying the bag is only showing motion,
where as the other is applying an
upward force to lift the bag up.
Back to question
HOW MUCH WORK?


20 N X .5m =

10 joules of work
man’s arms

10 N X .5m =


5 joules of work
man’s legs

60 N X 25m =

Back to question
1500 joules of work